The present disclosure relates generally to information handling systems, and more particularly to techniques for providing power from battery and system power sources commonly used in portable information handling system devices such as notebook computers, personal digital assistants, cellular phones and gaming consoles.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
A battery converts chemical energy within its material constituents into electrical energy in the process of discharging. A rechargeable battery is generally returned to its original charged state (or substantially close to it) by passing an electrical current in the opposite direction to that of the discharge. Presently well known rechargeable battery technologies include Lithium Ion (LiON), Nickel Cadmium (NiCd), and Nickel Metal Hydride (NiMH). In the past, the rechargeable batteries (also known as “dumb” batteries) provided an unpredictable source of power for the portable devices, since typically, a user of the device powered by the battery had no reliable advance warning that the energy supplied by the rechargeable battery was about to run out.
In absence of an AC power source, a battery ‘pack’ typically powers the portable information handling system device. The battery ‘pack’ typically includes a plurality of rechargeable battery cells arranged in a convenient, modular package. The battery pack is generally housed within the portable device in a detachable way. The plurality of battery cells are collectively referred to as a ‘stack’ and the voltage measured across the stack is referred to as a stack voltage.
Today, through the development of “smart” or “intelligent” battery packs, batteries have become a more reliable source of power by providing information to the information handling system and eventually to a user as to the state of charge, as well as a wealth of other information. The “smart rechargeable battery”, which is well known, is typically equipped with electronic circuitry to monitor and control the operation of the battery.
It is desirable to maximize the amount of time a portable device may be used in a battery-operated mode. Various well-known power management tools and methods of extending the time of use of batteries exist. For example, one technique uses dual smart batteries in the portable devices as a means to extend the battery life. The following U.S. patents describe various aspects of using “dual” smart batteries and are incorporated herein by reference: Selection Circuit For Dual Batteries In A Battery Powered Electronic Device (U.S. Pat. No. 5,867,007), Dual Smart Battery Detection System And Method For Portable Computers (U.S. Pat. No. 5,818,200), and Increased Battery Capacity Utilizing Multiple Smart Batteries (U.S. Pat. No. 6,262,562), and Smart Battery Selector Offering Power Conversion Internally Within A Portable Device (U.S. Pat. No. 5,903,764).
In some dual smart battery systems, a removable media peripheral device such as a 3.5″ floppy or an optical disk drive may be removed from a removable bay and replaced with a secondary or backup smart battery. The form factors of the primary and secondary primary batteries may vary. The secondary battery is capable of providing power to the portable device. In dual battery systems, problems may arise when the characteristics of two smart batteries used are different. For example, differences in number and types of cells and voltage per cell between two battery packs often result in a difference of output voltage level. Dell Computer Corporation (Round Rock, Tex., USA) provides 4 Series & 3 Series smart batteries for use in notebook computers. The 4SXP smart battery having a stack voltage of (12V-16.8V) and the 3SXP smart battery having a stack voltage of (9V-12.6V) are examples of a primary and secondary smart battery that may be used to power a device such as a Dell Lattitude™ D-Series dual battery notebook computer.
Typically when the stack voltages are dissimilar, the higher voltage pack will discharge first until it reaches approximately 0.4V above the other at which time the two battery packs will discharge in parallel via diodes. A problem arises when 4SXP smart battery having a stack voltage of (12V-16.8V) and the 3SXP smart battery having a stack voltage of (9V-12.6V) are selected as the primary and secondary smart batteries. In this case, the ‘primary’ smart battery will be selected for discharge first since it has the higher stack voltage. The primary smart battery continues to discharge to depletion. Upon depletion, the secondary smart battery having the lower stack voltage is switched on to continue to provide the power to the portable device. While operating in this mode, the user typically has limited visibility to the power available from the dual battery system. The visibility may be in the form of a battery icon displayed on a task bar of the device. The battery icon typically shows combined available power of the dual battery system and not the individual power for each of the smart batteries. The user is unaware that the primary smart battery has been critically discharged and the portable device is operating on the secondary smart battery. The user continues to observe the battery icon on a display of the portable device indicating that sufficient battery capacity is available to power the portable device even though the primary smart battery has been critically discharged. If the user elects to swap out the secondary smart battery with the removable media, the portable device experiences an immediate shutdown with possible loss of critical data.
Thus, the simultaneous presence of two or more batteries, especially smart batteries having different voltages, imposes certain difficulties in the operation of the dual battery system. Failure to deploy certain techniques may result in sudden loss of power and data, and hence in reduced reliability.
Therefore, a need exists to develop tools and techniques for providing more reliable power from battery and system power sources used in portable devices. More specifically, a need exists to develop tools and techniques for selectively discharging a dual battery system that is less expensive and more reliable than such systems and methods heretofore available. Accordingly, it would be desirable to provide tools and techniques for selectively discharging a dual battery system included in an information handling system absent the disadvantages found in the prior methods discussed above.